The invention relates to a method for communication by radio using a frequency band subdivided into a plurality of subbands.
In radio communication systems, communications such as voice information, image information, video information, SMS (Short Message Service), MMS (Multimedia Messaging Service) or other data are transmitted using electromagnetic waves across a radio interface between transmitting and receiving station. These stations can be various kinds of user stations or network-side installations such as repeaters, radio access points or base stations, depending on the specific implementation of the radio communication system. In a mobile communication system, at least some of the user stations are mobile stations. The electromagnetic waves are radiated using carrier frequencies which lie within in the frequency band intended for the particular system.
Such mobile communication systems are often implemented as cellular systems e.g. in accordance with the GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunications System) standard, having a network infrastructure including of base stations, equipment for monitoring and controlling the base stations, and other network-side equipment. Another example are broadband networks with wireless access in accordance with IEEE 802.16, for example. Future mobile communication systems can be e.g. refinements of UMTS, known as LTE (Long Term Evolution), or fourth generation systems, and also ad-hoc networks. Aside from supralocal cellular hierarchical radio networks, there exist wireless local area networks (WLANs) with generally much more limited coverage. Examples of different standards for WLANs are HiperLAN, DECT, IEEE 802.11, Bluetooth and WATM.
In radio communication systems, access to the common transmission medium by user stations is controlled by multiple access methods/multiplex methods (MA). For these multiple accesses, the transmission medium can be shared between the user stations in the time domain (Time Division Multiple Access, TDMA), in the frequency domain (Frequency Division Multiple Access, FDMA), in the code domain (Code Division Multiple Access, CDMA) or in the space domain (Space Division Multiple Access, SDMA). Combinations of multiple access methods are also possible, e.g. a frequency domain access method can be combined with a code domain access method.
In order to maximize data transfer efficiency, the entire available frequency band can be split up into plurality of subbands (multicarrier method). The basic idea of multicarrier systems is to recast the initial problem of transmitting a broadband signal into one of transmitting a plurality of narrowband signals. One of the advantages of this approach is that it enables receiver complexity to be reduced. In addition, the splitting-up of the available bandwidth into a plurality of narrowband subbands allows much higher data transmission granularity in respect of the distribution of the data to be transmitted among the different subbands, i.e. the radio resources can be more finely distributed over the data to be transmitted or more specifically between the user stations. Particularly in the case of variable rate data transmission or bursty data traffic, the available bandwidth can be efficiently utilized by allocating a plurality of subbands to different user stations. One example of a multicarrier transmission method is OFDM (Orthogonal Frequency Division Multiplexing) in which timewise approximately rectangular pulse shapes are used for the subbands.